There is almost an endless number of physical and chemical processes employed today wherein proper and efficient operation depends upon accurate measurements and the implementation of controls based on these measurements. Millions, perhaps billions, of dollars have been spent in this area, and yet there persists two very basic problems. First, and this may come as some surprise, many of the transducers which are employed to translate physical effects into electrical quantities are actually unreliable. A survey of a number of plants has revealed that because of this, instrument readings are frequently ignored and equipment and processing operated largely by guesswork. Where there is provided both the option of automatic control of equipment or process based upon the measurement of a physical quantity by a transducer, often an operator, distrusting the transducer, will opt for manual operation despite the known frailities of man in effecting control simply by sensory perceptions.
The second problem is that of the tremendous cost necessary to install and service measurement and control systems. A conventional system would employ an electrical circuit from a central control point to perhaps a hundred or so monitoring points, e.g., an atomic power plant or a pulp and paper mill, the use hundreds or thousands of feet of communications cable and a like quantity of electrical cable, both being quite expensive, the latter being very expensive to install.
The sad conclusion is, however, that even when a conventional system is installed at tremendous cost, it is often not long after installation that erratic measurements are experienced. One of the worst things is that failures, particularly drift type failures, are usually quite unpredictable, and the nature of these failures are not readily or conveniently ascertainable.
It is the object of this invention to deal with both problems and to provide a system which is adapted to both measure and control a system of equipment or processes with greatly enhanced accuracy and to actually reduce the cost of the overall installation.